Up until now, there have been proposed a wide variety of conventional acoustic feedback suppression apparatuses of this type. One typical example of the conventional acoustic feedback suppression apparatuses is disclosed in Japanese Patent Laid-Open Publication No. 07-143034 (see page 4 and FIG. 1).
The conventional acoustic feedback suppression apparatus 50 is shown in FIG. 5 as comprising an input terminal 1 having a sound signal inputted therein, an AD converter 2 for carrying out analog-to-digital conversion of the sound signal, a notch filter 3 connected to the AD converter 2, a DA converter 4 for carrying out digital-to-analog conversion of the sound signal, an output terminal 5 having the sound signal outputted therethrough, an FFT 6 for converting the sound signal outputted from the notch filter 3 into digital data with a predetermined number of data samples to perform a frequency analysis of the digital data, a determining unit 7 for determining the result of the analysis performed by the FFT 6, coefficient storing means 8 for storing therein prepared coefficients of the notch filter 3, a memory 9 for memorizing therein the coefficients of the notch filter 3, and coefficient selection means 10 for selecting the coefficients to be transferred to the memory 9 from among the coefficients stored in the coefficient storing means 8.
In the operation of the conventional acoustic feedback suppression apparatus 50, the frequency analysis of the sound signal outputted from the notch filter 3 is firstly performed by the FFT 6. The acoustic feedback characteristic of the sound signal, such as for example a peak frequency, is then determined by the determining unit 7, and only the specific coefficients each having a center frequency equal to the peak frequency determined by the determining unit 7 are selected by the coefficient selection means 10 from among the coefficient stored in the coefficient storing means 8. The coefficients thus selected are then transferred to the memory 9 by the coefficient selection means 10 before acoustic feedback components are filtered by the notch filter 3 specified with the coefficients out of the sound signal.
As will be seen from the above mentioned description, the conventional acoustic feedback suppression apparatus 50 is designed to suppress the acoustic feedback in the sound signal by specifying the filter coefficients of the notch filter 3 in response to the acoustic feedback characteristic of the sound signal.
The conventional acoustic feedback suppression apparatus thus constructed as previous mentioned, however, encounters such a problem that a relatively large number of data samples are required for performing the frequency analysis to specify the coefficients of the notch filter with high accuracy in the conventional acoustic feedback suppression apparatus. This leads to the fact that, when the conventional acoustic feedback suppression apparatus simultaneously suppresses the acoustic feedback in sound signals respectively inputted to a plurality of channels, the data-processing load of the frequency analysis becomes heavy with the number of the channels increased, thereby needing the memory with high-capacity.
It is, therefore, an object of the present invention to provide an acoustic feedback suppression apparatus which can lessen the data-processing load of the frequency analysis and decrease the capacity of the memory even if simultaneously suppressing the acoustic feedback of the sound signals respectively inputted to a plurality of channels.